The present invention relates generally to the field of candle making and in particular to a new and useful holder for a wick which extinguishes the candle flame at the end of the candle useful life.
Candle wicks function by capillary action drawing a fuel from a pool up through the wick to the flame. The fuel used in known candles may be paraffin wax, vegetable-based wax or synthetic polymers, like ester-terminated polyamides (ETPA), such as one sold under the name UNICLEAR, or PENRECO gel sold by Pennzoil. Paraffin waxes typically form a melt pool at between 150-200° F., while UNICLEAR polyamide forms a melt pool at between about 200-250° F. The capillary action can be through a fabric or thread wick or through a capillary tube. When the candle fuel pool becomes very shallow, it can become hot enough to vaporize and it no longer needs a wick to burn. This phenomenon is called “flash” or “flashover” and is a problem especially with candles formed or supported in containers.
Once the upper surface of the wax descends nearly to the floor of the container, the shallow pool of wax can be elevated above its flashpoint temperature, typically between 350-450° F. for conventional paraffin waxes and about 440° F. for UNICLEAR, for example. During flashover, the temperature within the candle can be elevated to at least 1200° F. This excessive heat can cause glass containers to break, and it can cause metal tins to scorch the paint off the tin sides and char surfaces on which they are resting. With freestanding candles the molten wax pool must not extend through the candle floor, because wax can flow out onto the candle supporting surface. If the wax flows out or the container of a contained candle breaks, supporting or surrounding objects can be ignited.
An additional problem is that carbon balls may form during burning and fall into the wax pool at the bottom of the candle, or the user may allow matches or wick trimmings to fall to the bottom. These foreign objects may aggravate the flashover problem by becoming secondary wicks if they are ignited by the candle flame.
In conventional candles formed in containers, a wick support like the sustainer 2 shown in FIG. 1, is often used to provide lateral support to a wick in a candle to hold the wick in place during pouring of the wax or other fuel. The sustainer 2 also keeps the wick standing upright when the supporting wax around the wick burns very low. The wick is held in a bore formed completely through the sustainer.
Sustainers of this type are popular for use in candles because they are easily assembled using machines. The wick is simply inserted through the bore and held in place by crimping the bore. The cylindrical plate of the sustainer 2 is easily affixed to a container for holding a candle.
During burning, molten wax 4 is drawn upwardly through the wick sides initially, and is carried to the flame. As the upper surface of the molten wax 4 descends to near the top end of the sustainer 2, the heat from the flame liquifies the wax all around the sustainer 2. Once this wax is liquified, molten wax 4 can be drawn from beneath the sustainer 2 through the bore and upwardly to the flame. This permits the majority of the wax 4 to be consumed before the flame goes out from lack of fuel. When the depth of the molten wax 4 is sufficiently small, the flashover problem can occur.
Flashover is a problem which causes significant damage and harm. Flashover can result in house fires and burns to people who use candles decoratively. This is a problem which is being given more attention by consumer groups and needs to be solved in an economical way. The need exists for an inexpensive and simple safety device for preventing or significantly decreasing the likelihood of flashover.
Several different approaches to solving the problem of flashover have been provided. U.S. Pat. No. 5,842,850, for example, discloses several embodiments of a wick sustainer of the type shown in FIG. 1 having the bottom end of the sustainer sealed against permeation by a candle fuel. The sealed bottom prevents molten candle fuel from being drawn through the wick in the bore of the wick sustainer, causing the candle to extinguish when the fuel level drops below the level of the exposed wick above the wick sustainer.
U.S. Pat. No. 4,332,548 teaches a transparent safety disc at the bottom of a candle. The safety disc is formed by a thermoplastic polyamide resin, combined with a flammable solvent for the resin that is compatible with the candle material. The candle is also transparent. A wick holder and wick are placed on a layer of the resin mixture followed by pouring the candle material around the wick and wick holder and over the resin layer. The safety disc layer helps prevent flameups due to its higher melting point and other characteristics which render it substantially non-flammable in the presence of a candle flame.
U.S. Pat. No. 3,797,990 discloses a safety layer for a candle formed from a higher melting point wax. The higher melting point wax in the safety layer is not combustible by a candle flame. The safety layer may be positioned around or below the wick clip and wick bottom. When the candle flame nears the safety layer and causes it to melt, the wax in the safety layer begins to block the wick, subsequently resulting in the candle flame being extinguished due to lack of fuel.
U.S. Pat. No. 2,831,330 teaches adding polybutene polymers to a candle wax in different proportions to first extend the burn time of the candle and then in an amount sufficient to extinguish the candle due to lack of fuel. Polybutene polymer provided in concentrations of about 15% in a portion of a candle is disclosed as being capable of extinguishing a candle when the candle flame reaches the area of higher polybutene concentration.
U.S. Pat. No. 5,127,922 describes a candle having an outer shell which includes 10-30% of a fire retardant material. The fire retardant material is mixed with a thermoplastic compound, so that the shell will slowly melt and mix with the candle fuel as the candle burns. The fire retardant can be a silicone elastomer, a non-halogenated, inorganic flame retardant or an alumina trihydrate, among other compounds.
Other mechanical devices for extinguishing a candle prior to the point where a flashover or flame-up would occur are known, such as taught by U.S. Pat. No. 4,818,214 for a candle having a heat-shrinkable sleeve around the candle near the base. When the candle burns down sufficiently that the candle flame is near the sleeve, the heat activates the sleeve, causing it to shrink inwardly, constricting the wick and extinguishing the flame.
Several of the prior art devices and compounds use flame retardants or flame-resistant materials to extinguish the flame. But, the prior compounds and apparatus for preventing flashover or extinguishing a candle flame can be complex and require particular mixtures of components. Further, some prior art flame-retardant coatings and mixtures for use on wicks or in candle fuels can also make the candle difficult to use by extinguishing the candle prematurely and requiring relighting well before the end of the useable life.
Polyethylene discs with central bores for holding wicks have been suggested for use as the wick holder in a candle to prevent flashover. However, testing has revealed that polyethylene discs soften at 200° F. and can combust rather easily when exposed to a burning candle flame. Thus, polyethylene, while easy to mold, is not suitable for providing a non-combustible wick holder for extinguishing a candle flame at the end of the candle useful life.
Clearly, few simple solutions for preventing flashover which are easy to manufacture and incorporate into a candle are available.
A flame-resistant and retardant wick holder which can be easily incorporated into candles in place of existing wick sustainers is needed. Plastics are a material which can be easily molded and formed, but which can also combust and produce very toxic by-products.
A widely accepted test to determine flammability of plastics used in products is found in Underwriter Laboratories UL-94 standard. ASTM standard 3801-96 and ISO standard 1210-1991 are similar standards having similar tests and equivalent ratings.
The UL-94 standard includes horizontal and vertical burn tests which can be used to rate the flammability of plastics. The vertical burn test is considered more stringent and a plastic can receive one of several ratings, depending on its flammability.
A rating of V-0 from the UL-94 vertical burn test indicates that combustion of the product stops within ten seconds after two applications of ten seconds each of a flame to a test bar of the plastic material, and the material must not produce any flaming drips. The V-0 rating is considered the best rating of non-flammability for a plastic.
The UL-94 vertical burn test is performed by suspending a ½ inch wide by 5 inch long test rod of the plastic material over a cotton pad. A burner flame is applied to the lower end of the test rod for ten seconds, following which combustion of the rod, if any is observed until it stops. The burner flame is applied to the test rod for a second period of ten seconds. Observations of the test rod following application of the flame determine the rating the material will receive. In addition to the requirements noted above, the specimen must not begin glowing or flaming combustion after application of the burner flame. The rating for the material is based on the thickness of the test rod used. That is, a ¼ inch thick test rod which achieves a V-0 rating qualifies the material of the test rod used in products in ¼ or greater thicknesses. The thinner the test rod, the less combustible the material.
Polyethersulfone (PES) is one such material which has a V-0 rating for the UL-94 vertical burn test at a thickness of 0.8 mm, or about 1/32 inches. Polyethersulfone is a thermoplastic material which is commonly used for electrical applications such as wire insulation, connectors, molded interconnects and housings for starters. Polyethersulfone is also known for use in other applications as well where heat resistance is desired. However, while the combustion characteristics of polyethersulfone are known, PES is not known for use in applications involving open flames.